Captcha

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PowerPoint Presentation:

captcha PRASENTED BY BHANU.S

AGENDA:

AGENDA Introduction History of CAPTCHA Types of CAPTCHAs Constructing CAPTCHAs Breaking CAPTCHAs Application of CAPTCHAs Issues with CAPTCHAs Conclusion

CAPTCHA STANDS FOR :

CAPTCHA STANDS FOR C -COMPLETELY A -AUTOMATED P -PUBLIC T -TURING TEST TO TELL C -COMPUTERS AND H -HUMANS A - APARTS

INTRODUCTION:

INTRODUCTION Completely Automated Public Turing test to tell Computer and Human Aparts This is full form of CAPTCHA and also define the purpose of CAPTCHA Actually CAPTCHA is used as simple puzzle hurdle Which restricts various automated program to sign up E-mail accounts, cracking passwords, spam sending,

PowerPoint Presentation:

Cont…. CAPTCHA is trying to access some private zone! This challenge of CAPTCHA is not complicated problem Actually CAPTCHA is simply some visual test or some puzzle test The CAPTCHA test include some code in from of some images letters, alphabets, numbers,etc

HISTORY:

HISTORY The term “CAPTCHA” was coined in 2000 by luis von ahn,manuel blum, and nicholas j.hopper and john langford Actually the concept of CAPTCHA is motivated by real-world problem faced by internet companies such as yahoo and aita vista This companies offer fee email account ,intended for use by humans

Cont…..:

Cont….. If user to pass the captcha test ,we will enter the E-mail account The CAPTCHA used by yahoo, yahoo used to two types of CAPTCHAs 1.gimpy 2.ez-gimpy this both are word based captcha

Types of CAPTCHAs:

Types of CAPTCHAs GIMPY EZ-GIMPY PIX BONGO

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Gimpy: Designed by Yahoo Picks up 10 random words from dictionary and distorts, fills with noise User has to recognize at least 3 words If user is correct, he is admitted The more difficult version of the gimpy CAPTCHA presents an image such as the one shown diagram

EXAMPLE OF GIMPY:

EXAMPLE OF GIMPY

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EZ-Gimpy : A modified version of Gimpy Yahoo used this version in Messenger Has only 1 random string of characters Not a dictionary word, so not prone to dictionary attack Not a good implementation, already broken by OCRs

EXAMPLE OF EZ-GIMPY:

EXAMPLE OF EZ-GIMPY

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MSN’s Passport service CAPTCHAs : Provided for Microsoft’s MSN services Use 8 characters Warping is used to distort Very strong implementation, hasn’t been broken It is segmentation-resistant

EXAMPLE:

EXAMPLE

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Graphic based CAPTCHAs : BONGO : It is sound based captcha After M.M.Bongard , pattern recognition expert User has to solve a pattern recognition problem Has to tell the distinct characteristic between two sets of figures Then tell to which set a given figure belongs to

EXAMPLE:

EXAMPLE

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PIX: Uses a large database of labelled images It shows a set of images, user has to recognize the common feature among those E.g., Pick the common characteristic among the following four pictures-----” Aeroplane ”

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Audio CAPTCHAs : Consist of downloadable audio clip User listens and enters the spoken word Helps visually disabled users Below is the Google’s audio enabled CAPTCHA Not popular

EXAMPLE:

EXAMPLE

Constructing CAPTCHAs:

Constructing CAPTCHAs Things to keep in mind : Don’t store CAPTCHA solution in Web page’s metadata A CAPTCHA is no good if it doesn't distort Need a large database of different CAPTCHA questions avoid repetition of questions

Cont……:

Cont…… Custom CAPTCHAs Fits to the theme of page Better protected from spammer Embedded of CAPTCHA Available freely ,just embed code into webpage's html,from eg:www.recaptcha.net No maintenance

PowerPoint Presentation:

CAPTCHA Logic : Generate the question Persist the correct answer Present the question to user Evaluate answer, if incorrect, start again-- Generate a different CAPTCHA If correct, allow access to user

Breaking CAPTCHAs:

Breaking CAPTCHAs 3 steps are used to break the captcha Step 1: Locate possible letters at various location Step 2: Construct graph of consistent letter Step 3: look for possible words in graph

Applications:

Applications Protect online polls Prevent Web registration abuse, protect passwords from brute-force attack Prevent comment spam and spam emails Preventing dictionary attacks.

Issues with CAPTCHAs:

Issues with CAPTCHAs 1.USABILITY OF TEXT BASED 2.USABILITY OF AUDIO BASED

USABILITY WITH TEXT BASED:

USABILITY WITH TEXT BASED This issues are text captcha like gimpy, sometimes the text is distorted to such an extent that even human have difficulty in number standard it, some of issues are listed in table “d” can be confused for “cl” “m” can be confused for “rn” Font and colors to confused

Usability of audio based:

Usability of audio based Noises are deliberately added to prevent back ground noises effectively distort sound in audio captcha

Conclusion:

Conclusion CAPTCHAs are an effective way to counter bots and reduce spam CAPTCHAs as useful as data sets for studying object recognition They serve dual purpose– help advance AI knowledge Applications are varied– from stopping bots to character recognition & pattern matching Some issues with current implementations represent challenges for future improvements

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